Polarization rotation beam splitter
By employing a layered waveguide structure in the polarization rotating beamsplitter and utilizing a fully etched waveguide design, asymmetric mode rotation and separation are achieved, solving the problem of low design freedom in existing technologies and realizing a high-efficiency polarization rotating beamsplitter design with low crosstalk and low loss.
Patent Information
- Application Number
- CN202511188729.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-25
- Publication Date
- 2025-11-18
AI Technical Summary
In the existing technology, polarization rotating beam splitters are designed by etching a single-layer optical waveguide at different depths multiple times to change the waveguide shape. This results in low design freedom and makes it difficult to meet complex performance requirements such as low crosstalk, low loss, and high optical power carrying capacity.
A layered first and second waveguide structure is adopted. The light is split into two beams by mutual coupling of the waveguides on both sides of the waveguide layer. Mode rotation and separation are achieved by constructing asymmetry. Specifically, the first waveguide and the second waveguide are asymmetrical in the first direction. The full etched waveguide design is used to reduce the precision requirements of the etching depth.
It achieves efficient mode rotation and separation, reduces optical loss, improves device performance stability and process compatibility, and is suitable for multilayer SiN-on-Si platforms.
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Figure CN120972383A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of optical fiber communication, in particular to a polarization rotation beam splitter. BACKGROUND
[0002] With the rapid development of generative artificial intelligence, large language models and other technologies, the demand for hardware computing power is growing exponentially. Integrated optics technology, with its natural optical parallelism, low power consumption and compatibility with CMOS technology, has become an important technical direction to break through the performance bottleneck of traditional electronic chips. In optical interconnection, optical computing and other application scenarios, the silicon photonics platform has shown the potential for high-density integration.
[0003] Polarization multiplexing technology can significantly improve the channel capacity of on-chip optical systems through orthogonal polarization state transmission. The core of this technology is to take advantage of the independence of the transverse electric mode (TE mode) and the transverse magnetic mode (TM mode) in the optical waveguide, to realize double independent signal transmission in the same physical channel, which can theoretically double the transmission capacity. Compared with traditional single polarization transmission schemes, polarization multiplexing can break through the mode density limit of a single polarization state without additional waveguide quantity or chip area, and has become a key technology path to improve the spectral efficiency of integrated optoelectronic systems.
[0004] In the field of optical fiber communication, polarization multiplexing has been combined with wavelength division multiplexing (WDM) technology to achieve a single fiber capacity from Tbps to Pbps. However, in the on-chip integration scenario, due to the strong mode constraint characteristics of nanoscale waveguides, key technologies such as mode crosstalk suppression between orthogonal polarization states, efficient polarization state conversion and separation face severe challenges. Specifically, the on-chip polarization multiplexing system needs to precisely control the effective refractive index difference, mode field distribution and coupling efficiency of the TE / TM mode, which puts higher requirements on the precision of device structure design and process compatibility. Therefore, developing high-performance on-chip polarization multiplexing devices has become a key technical breakthrough to realize high-density photonic integration and meet the needs of intelligent computing and high-speed communication.
[0005] Currently, the mainstream silicon-on-chip polarization rotation beam splitter is mainly based on a single-layer silicon waveguide structure, which requires the introduction of an asymmetric type to achieve polarization rotation and separation. There are two specific methods: one is the geometric deformation method, which introduces the geometric asymmetry required for mode coupling by asymmetrically etching the waveguide (such as trapezoidal, wedge-shaped, ridge-shaped structure); the second is the refractive index regulation method, which uses the refractive index difference between the coating layer and the buried oxygen layer to build a mode conversion system.
[0006] But in the multi-layer SiN-on-Si platform, the use of different refractive index coating layers needs to customize the process, and there are process reliability risks such as chip warping. At present, the polarization rotation beam splitter is usually designed by etching a single-layer optical waveguide multiple times with different depths to change the shape of the waveguide. This method has low design freedom and is difficult to meet the complex performance requirements of low crosstalk, low loss, high optical power bearing, etc. SUMMARY
[0007] Therefore, it is necessary to provide a polarization rotation beam splitter to solve the problem that the prior art polarization rotation beam splitter is designed by etching a single-layer optical waveguide multiple times with different depths to change the shape of the waveguide, resulting in low design freedom and difficulty in meeting the complex performance requirements of low crosstalk, low loss, high optical power bearing, etc.
[0008] In one aspect, the present application provides a polarization rotation beam splitter, comprising a first waveguide layer and a second waveguide layer layered in a first direction; each waveguide layer comprises at least one waveguide; the first waveguide layer comprises a first waveguide, the first waveguide comprising an input end and a first output end; the second waveguide layer comprises a second waveguide, the second waveguide comprising a second output end; the second waveguide is asymmetric with the first waveguide in the first direction; the light entering the first waveguide from the first input end is coupled through the first waveguide and the second waveguide, and then output along the first output end and the second output end.
[0009] Optionally, the first waveguide comprises an input section, a first coupling section and a first output section connected in sequence in a second direction; wherein the size of the input section, the first coupling section and the first output section in the first direction is the same, and the size of the first coupling section in a third direction is greater than the size of the input section or the first output section in the third direction; wherein the first direction, the second direction and the third direction are perpendicular to each other.
[0010] Optionally, the size of the first coupling section in the third direction is less than or equal to 3μm.
[0011] Optionally, the first coupling section and the input section have a first transition section, and the size of the first transition section in the third direction gradually increases from the same size as the input section to the same size as the first coupling section; the first coupling section and the first output section have a second transition section, and the size of the second transition section in the second direction gradually decreases from the same size as the coupling section to the same size as the output section.
[0012] Optionally, the second waveguide comprises a second coupling section and a second output section connected along the second direction; the cross-sectional dimensions of the second coupling section and the second output section are the same; in the third direction, the distance between the first output section and the second output section is greater than the distance between the first coupling section and the second coupling section.
[0013] Optionally, the distance between the second coupling section and the first coupling section in the first direction is less than or equal to 500 nm.
[0014] Optionally, a third transition section is further connected between the second coupling section and the second output section.
[0015] Optionally, at least one secondary light path waveguide is further included, each of the secondary light path waveguides is located at the side of the second waveguide, and the distance between each of the secondary light path waveguides and the second waveguide in the first direction is less than or equal to 500 nm, and the distance between each of the secondary light path waveguides and the second waveguide in the third direction is less than or equal to 500 nm.
[0016] Optionally, the at least one secondary light path waveguide is located on the first waveguide layer and is located at the side of the first waveguide close to the second waveguide.
[0017] Optionally, the at least one secondary light path waveguide is located on the second waveguide layer, and all the secondary light path waveguides are located at the same side of the second waveguide.
[0018] Optionally, a third waveguide layer is further included, the third waveguide layer is located at the side of the second waveguide layer away from the first waveguide layer, and the at least one secondary light path waveguide is located on the third waveguide layer.
[0019] Optionally, the first waveguide, the second waveguide and the secondary light path waveguide have a size of 200-500 nm in the first direction.
[0020] The polarization rotation beam splitter of the present application is divided into two waveguide layers, and a beam of light is split into two beams and then outputted through the mutual coupling of the waveguides on the two waveguide layers. Specifically, the TE0 mode light enters the input end of the first waveguide and is directly outputted from the first output end of the first waveguide, the TM0 mode light enters the input end of the first waveguide and is finally converted into the TE0 mode light of the second waveguide through the mutual coupling of the second waveguide and the first waveguide, and then the TE0 mode light is outputted through the second output end. In addition, the second waveguide of the present application is asymmetric in the first direction, i.e., the asymmetricity is constructed in the vertical propagation plane structure layering manner, the mode rotation is realized, and the mode separation efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS
[0021] Figure 1 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application.
[0022] Figure 2 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application. Figure 1 A schematic diagram of a cross-sectional structure according to an embodiment of the present application.
[0023] Figure 3 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application.
[0024] Figure 4 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application. Figure 3 A schematic diagram of a cross-sectional structure according to an embodiment of the present application.
[0025] Figure 5 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application. Figure 3 A schematic diagram of a cross-sectional structure according to an embodiment of the present application.
[0026] Figure 6 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application.
[0027] Figure 7 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application.
[0028] Figure 8 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application.
[0029] Figure 9 A schematic diagram of a polarization-rotating beam splitter according to an embodiment of the present application.
[0030] Figure 10 A schematic diagram of a cross-sectional structure and a mode field distribution of a polarization-rotating beam splitter according to an embodiment of the present application; wherein (a) is a symmetric mode field distribution, and (b) is an anti-symmetric mode field distribution.
[0031] Figure 11 A schematic diagram of a mode field distribution in an xy plane of a polarization-rotating beam splitter according to an embodiment of the present application; wherein (a) is a mode field distribution of light transmission of a TE0 mode, and (b) is a mode field distribution of light transmission of a TM0 mode.
[0032] Figure 12 A schematic diagram of a transmission spectrum of a polarization-rotating beam splitter according to an embodiment of the present application; wherein (a) is a transmission spectrum of a TE0 mode of light input into the polarization-rotating beam splitter, and (b) is a transmission spectrum of a TM0 mode of light input into the polarization-rotating beam splitter.
[0033] Explanation of reference signs Polarization-rotating beamsplitter - 100; first waveguide - 110; input - 111; first output - 112; input section - 113; first coupling section - 114; first output section - 115; first transition section - 116; second transition section - 117; Second waveguide - 120; second output - 121; second coupling section - 122; second output section - 123; third transition section - 124; secondary optical path waveguide - 130; silicon oxide - 140. DETAILED DESCRIPTION
[0034] For the technical solutions and advantages of the present application to be more obvious and easy to understand, the following will be described in detail by listing specific embodiments. The drawings are not necessarily drawn to scale, and local features can be enlarged or reduced to more clearly show the details of local features; unless otherwise defined, the technical and scientific terms used herein have the same meaning as the technical and scientific terms in the technical field to which the present application belongs.
[0035] As a specific embodiment of the present application, as shown in Figure 1 and Figure 2 The present embodiment provides a polarization-rotating beamsplitter 100, which can include a first waveguide layer and a second waveguide layer layered in a first direction (i.e., the direction indicated by the arrow z in the figure). Each waveguide layer includes at least one waveguide. The first waveguide layer includes a first waveguide 110, which includes an input 111 and a first output 112. The second waveguide layer includes a second waveguide 120, which includes a second output 121. The second waveguide 120 is asymmetric with the first waveguide 110 in the first direction. Light entering the first waveguide 110 from the input 111 is coupled through the first waveguide 110 and the second waveguide 120 and is output along the first output 112 and the second output 121.
[0036] Specifically, the polarization-rotating beam splitter 100 of the embodiment is divided into two waveguide layers, and a beam of light is split into two beams and then outputted through the mutual coupling of waveguides on the two waveguide layers. Specifically, the TE0 mode light enters the input end 111 of the first waveguide 110 and is directly outputted from the first output end 112 of the first waveguide 110, and the TM0 mode light enters the input end 111 of the first waveguide 110 and is finally converted into the TE0 mode light of the second waveguide 120 through the mutual coupling of the second waveguide 120 and the first waveguide 110, and then the TE0 mode light is outputted from the second output end 121. In addition, the second waveguide 120 of the embodiment is asymmetric to the first waveguide 110 in the first direction, that is, the asymmetricity is configured in the vertical propagation plane structure layering manner, the mode rotation is realized, the efficient mode rotation and separation are realized, and the polarization-rotating beam splitter 100 of the O, E, S, C, L, and U bands can be designed.
[0037] As a specific embodiment of the present application, the first waveguide 110 of the embodiment can include an input section 113, a first coupling section 114, and a first output section 115 connected in sequence in the second direction (i.e., the direction indicated by the arrow x in the figure). The input section 113, the first coupling section 114, and the first output section 115 have the same size in the first direction, and the first coupling section 114 has a size in the third direction (i.e., the direction indicated by the arrow y in the figure) greater than the size of the input section 113 or the first output section 115 in the third direction. The first direction, the second direction, and the third direction are perpendicular to each other.
[0038] Specifically, the second direction of the embodiment is the direction of light propagation.
[0039] The first waveguide 110 of the embodiment extends along the second direction, and the first waveguide 110 can include an input section 113, a first coupling section 114, and a first output section 115 connected in sequence in the second direction (x), which have the same size in the first direction and different sizes in the third direction. Therefore, only a single-step full etching in the first direction of the first waveguide 110 is required, and the control accuracy of the etching depth is low, which eliminates the dependence of the device on the etching accuracy of the different thicknesses of the optical waveguide.
[0040] In addition, the first waveguide 110 and the second waveguide 120 of the embodiment are full etching waveguides, which can be directly applied to the existing multi-layer SiN-on-Si process platform.
[0041] In addition, the first coupling section 114 has a dimension in the third direction greater than the dimensions of the input section 113 and the first output section 115, which can improve the effective refractive index of the TM0 mode light. The input end 111 and the first output section 115 have the same dimension in the third direction, so that the properties of the TE0 mode light output finally are not changed.
[0042] Specifically, the dimension of the first coupling section 114 in the third direction is not greater than 3 μm and not less than 100 nm. Generally, when the waveguide dimension is greater than 3 μm, multiple modes exist in the waveguide, which easily affects the working state of the polarization rotation beam splitter. In addition, the waveguide mode binding effect is good under a large dimension, which leads to poor coupling separation efficiency. When the dimension is less than 100 nm, the process is difficult and the process tolerance is small, and it is extremely challenging to achieve stable and controllable wafer-level consistency. Therefore, the dimension of the first coupling section 114 in the third direction is between 100 nm and 3 μm. Preferably, the dimension of the first coupling section 114 in the third direction is between 500 nm and 1.5 μm.
[0043] In order to avoid the need for high-precision etching of the input section 113 and the first output section 115 of the waveguide, the dimensions of the input section 113 and the first output section 115 in the third direction are also greater than 100 nm. Preferably, the dimensions of the input section 113 and the first output section 115 in the third direction are greater than 500 nm, but less than the dimension of the first coupling section 114 in the third direction.
[0044] Specifically, the first coupling section 114 and the input section 113 have a first transition section 116 therebetween, and the dimension of the first transition section 116 in the third direction gradually increases from the same as the dimension of the input section 113 to the same as the dimension of the first coupling section 114. The first coupling section 114 and the first output section 115 have a second transition section 117 therebetween, and the dimension of the second transition section 117 in the second direction gradually decreases from the same as the dimension of the coupling section to the same as the dimension of the output section.
[0045] In the embodiment, the transition sections are arranged between the input section 113 and the first coupling section 114 and between the first coupling section 114 and the first output section 115, and the dimensions gradually change, which avoids sudden changes in the waveguide dimension, avoids exciting additional high-order optical modes, and reduces additional optical loss caused by mode mismatch of light propagating in the first waveguide 110.
[0046] Specifically, the second waveguide 120 of the embodiment can include a second coupling segment 122 and a second output segment 123 connected along the second direction. The second coupling segment 122 and the second output segment 123 can have different sizes in the third direction to meet the specific coupling segment design. Preferably, the second coupling segment 122 and the second output segment 123 of the embodiment have the same cross-sectional size, and no additional waveguide size gradient is needed in the transition segment. In the third direction, the distance between the first output segment 115 and the second output segment 123 is greater than the distance between the first coupling segment 114 and the second coupling segment 122.
[0047] The distance between the second coupling segment 122 and the first coupling segment 114 of the embodiment is close, so that the first waveguide 110 and the second waveguide 120 are coupled at the positions of the first coupling segment 114 and the second coupling segment 122, and the TM0 mode light in the first waveguide 110 enters the TE0 mode in the second waveguide 120 through the coupling between the first coupling segment 114 and the second coupling segment 122 at the first coupling segment 114, and propagates along the second waveguide 120.
[0048] Specifically, the distance between the first coupling segment 114 and the second coupling segment 122 in the first direction of the embodiment is less than or equal to 500 nm, and the distance between the first coupling segment 114 and the second coupling segment 122 in the third direction also needs to be less than or equal to 500 nm. In this way, the first coupling segment 114 and the second coupling segment 122 can be coupled. Along the third direction, the distance between the second coupling segment 122 and the first waveguide 110 on the front side and the rear side of the second coupling segment 122 needs to be greater than 500 nm, so as to avoid the front side and the rear side of the second coupling segment 122 from being coupled with the first waveguide 110 and introducing additional optical loss.
[0049] Specifically, the second coupling segment 122 and the second output segment 123 of the embodiment are also connected by a third transition segment 124. Preferably, the cross-sectional sizes of the third transition segment 124, the second coupling segment 122, and the second output segment 123 are the same; the third transition segment 124 can adjust the waveguide spacing, so that the second output segment 123 is away from the first waveguide 110.
[0050] As a specific embodiment of the present application, as shown in Figure 3 and Figure 4 The polarization-rotating beam splitter 100 of the embodiment also includes at least one secondary light path waveguide 130. Each secondary light path waveguide 130 is located on the side of the second waveguide 120, and the distance between each secondary light path waveguide 130 and the second waveguide 120 in the first direction is less than or equal to 500 nm, and the distance between each secondary light path waveguide 130 and the second waveguide 120 in the third direction is less than or equal to 500 nm.
[0051] Specifically, the embodiment further provides at least one sub-optical path waveguide 130 on the side of the second waveguide 120, which is an auxiliary waveguide and can improve the coupling efficiency of the first coupling section 114 and the second coupling section 122, thereby realizing efficient polarization rotation and beam splitting.
[0052] Specifically, the size of the sub-optical path waveguide 130 is generally not higher than 500 nm, and the distance between the sub-optical path waveguide 130 and the second waveguide 120 in the first direction and the third direction is less than 500 nm. Preferably, the distance between the sub-optical path waveguide 130 and the second waveguide 120 in the first direction is 200-300 nm, and the distance in the third direction is less than 300 nm. Specifically, the distance between the sub-optical path waveguide 130 and the second waveguide 120 should not be too large, because too large distance has little auxiliary effect on the coupling performance of the second waveguide 120.
[0053] Specifically, the number of the sub-optical path waveguide 130 can be one or more. Regardless of the number of the sub-optical path waveguide 130, both the sub-optical path waveguides 130 are located on the same side of the second waveguide 120, and the distance between each sub-optical path waveguide 130 and the second waveguide 120 in the first direction and the third direction is less than 500 nm.
[0054] As one specific embodiment of the present application, as shown in Figure 4 and Figure 6 , the embodiment provides at least one sub-optical path waveguide 130 on the first waveguide layer and on the side of the first waveguide 110 close to the second waveguide 120. Specifically, as shown in Figure 6 , the sub-optical path waveguide 130 can include two sub-optical path waveguides 130, both of which are located on the first waveguide layer and on the same side of the first waveguide 110.
[0055] Specifically, when the sub-optical path waveguide 130 is located on the first waveguide layer, it is located on the side of the first waveguide 110 close to the second waveguide 120, and the sub-optical path waveguide 130 can coincide with the second waveguide 120 in the first direction.
[0056] Specifically, at this time, the sub-optical path waveguide has the same distance to the first coupling section 114 in the third direction as the second waveguide 120 at the position corresponding to the first coupling section 114 of the first waveguide 110, and the structure gradually moves away from the first waveguide 110 in other regions, and the size of the sub-optical path waveguide 130 gradually decreases until it does not exist (as shown in Figure 5 ).
[0057] As another specific embodiment of the present application, as shown in Figure 7 and Figure 8As shown, at least one sub-path waveguide 130 of the embodiment is located on the second waveguide layer, and all sub-path waveguides 130 are located on the same side of the second waveguide 120. When the sub-path waveguide 130 is located on the second waveguide layer, it is located on one side of the second waveguide 120 in the third direction. Similarly, the sub-path waveguide 130 has a size of less than 500 nm in the third direction. Similarly, the size gradually decreases at other positions until it disappears.
[0058] As another specific embodiment of the present application, as shown in Figure 9 As shown, the polarization rotation beam splitter 100 of the embodiment can further include a third waveguide layer located on the side of the second waveguide layer away from the first waveguide layer, and at least one sub-path waveguide 130 is located on the third waveguide layer.
[0059] Specifically, the first waveguide 110, the second waveguide 120 and the sub-path waveguide 130 of the embodiment have a size of 200-500 nm in the first direction. In the first direction, the sizes of the first waveguide 110, the second waveguide 120 and the sub-path waveguide 130 can be the same or different; in the third direction, the waveguides of different layers have different size differences according to actual conditions. Preferably, in the third direction, the size of the sub-path waveguide 130 in the coupling region is less than 500 nm; the sizes of the first waveguide 110 and the second waveguide 120 are greater than 500 nm.
[0060] Specifically, all waveguides of the embodiment are arranged in silicon oxide 140.
[0061] The positions of the first waveguide layer and the second waveguide layer in the first direction in the above embodiments can be exchanged, and no matter how the first waveguide layer and the second waveguide layer are exchanged, the third waveguide layer is located on the side of the second waveguide layer away from the first waveguide layer.
[0062] Specifically, the following is described by way of specific embodiments. Embodiment 1
[0063] Referring to Figure 1 and Figure 2From the surface of the optical chip downwards, the layers are a first waveguide layer and a second waveguide layer (or the positions of the first and second waveguide layers are interchanged). The entire optical waveguide structure is placed in oxide 140. Both TE0 and TM0 mode light are input from the input terminal 111 of the first waveguide 110. The TE0 mode light remains in its original state and passes through the input segment 113, the first transition segment 116, the first coupling segment 114, the second transition segment 117, and the output segment before being output from the first output terminal 112. The TM0 mode light, after passing through the input segment 113 and the first transition segment 116 to the first coupling segment 114, undergoes coupling between the first coupling segment 114 and the second coupling segment 122, changing its mode from TM0 to TE0. It then travels to the second waveguide 120 for transmission and finally passes through the second output segment 123 before being output from the second output terminal 121 in TE0 mode.
[0064] To enable coupling between the first waveguide 110 and the second waveguide 120, and to facilitate the conversion of the TM0 mode to the TE0 mode, precise design of the dimensions and spacing of the two waveguides is required. Therefore, before the first coupling section 114, the dimensions of the first waveguide 110 in the third direction need to gradually increase to improve the effective refractive index of the TM0 mode. After the first coupling section 114, the dimensions of the first waveguide 110 in the third direction need to gradually decrease to the width of a conventional transmission waveguide. The second waveguide 120 maintains the optimal waveguide dimensions required for coupling, but spacing adjustment is needed within the coupling region to achieve optimal spacing within the coupling region and prevent coupling outside the coupling region. This achieves efficient coupling of the corresponding modes within the coupling region.
[0065] In this embodiment, the dimensions of the first waveguide 110 in the first coupling section 114 are as follows: Figure 2 As shown, both the first waveguide 110 and the second waveguide 120 are made of silicon nitride. The thickness of the first waveguide 110 (i.e., the dimension in the first direction) is 300 nm. In the first direction, the distance between the first waveguide 110 and the second waveguide 120 is 200 nm. In the third direction, the distance between the first waveguide 110 and the second waveguide 120 is 150 nm. The width of the first waveguide 110 (the dimension in the third direction) is 1420 nm. The width of the second waveguide 120 (the dimension in the third direction) is 680 nm. Their symmetric and antisymmetric modes are as follows: Figure 10 (a) and Figure 10 As shown in (b), by Figure 10 (a) and Figure 10 (b) shows that this waveguide configuration can break the symmetry in the first direction, realizing the coupling of the TM0 mode of the first waveguide 110 and the TE0 mode of the second waveguide 120. Through simulation verification of this device, the mode field distribution diagrams of the double-layer silicon nitride waveguide polarization rotating beam splitter 100 in the first and third directions are shown below. Figure 11as shown in FIG. 1 (a). When the mode of the light input into the first waveguide 110 is TE0 mode, the light remains TE0 mode and is transmitted along the first waveguide 110 to the first output end 112, as shown in FIG. 1 (b). When the mode of the light input into the first waveguide 110 is TM0 mode, the light will be coupled to the TE0 mode of the second layer waveguide when the two layers of waveguides are close enough in the coupling region, as shown in FIG. 1 (c). Finally, the light is output in TE0 mode at the second output end 121, as shown in FIG. 1 (d). Figure 11 As shown in FIG. 2 (a), the light input in TM0 mode can be efficiently polarized and split, as shown in FIG. 2 (b). The light input in TE0 mode can be transmitted with low loss, as shown in FIG. 2 (c). The overall insertion loss of the device is less than 0.5 dB at 1310 nm, and the extinction ratio is greater than 25 dB. Figure 11 As shown in FIG. 3, the transmission spectrum of the dual-layer silicon nitride waveguide polarization-rotating beam splitter 100 is shown. The light input in TE0 mode can be transmitted with low loss (as shown in FIG. 3 (a)), and the light input in TM0 mode can be efficiently polarized and split (as shown in FIG. 3 (b)). Figure 12 As shown in FIG. 4, the transmission spectrum of the dual-layer silicon nitride waveguide polarization-rotating beam splitter 100 is shown. The light input in TE0 mode can be transmitted with low loss (as shown in FIG. 4 (a)), and the light input in TM0 mode can be efficiently polarized and split (as shown in FIG. 4 (b)). Figure 12 As shown in FIG. 5, the transmission spectrum of the dual-layer silicon nitride waveguide polarization-rotating beam splitter 100 is shown. The light input in TE0 mode can be transmitted with low loss (as shown in FIG. 5 (a)), and the light input in TM0 mode can be efficiently polarized and split (as shown in FIG. 5 (b)). Figure 12 As shown in FIG. 6, the transmission spectrum of the dual-layer silicon nitride waveguide polarization-rotating beam splitter 100 is shown. The overall insertion loss of the device is less than 0.5 dB at 1310 nm, and the extinction ratio is greater than 25 dB. Embodiment 2
[0066] As shown in FIG. 7, the full-etch silicon nitride polarization-rotating beam splitter 100 based on a dual-layer three-waveguide structure is shown. The device structure is shown in FIG. 8. Figure 3 As shown in FIG. 9, the first waveguide layer of this embodiment includes two waveguides, and the second waveguide layer includes one waveguide. All waveguides are in silicon oxide. The first layer waveguides are the first waveguide 110 and the secondary light path waveguide 130, and the second layer waveguide is the second waveguide 120. The second waveguide 120 of this embodiment is located directly below the secondary light path waveguide 130. In the coupling region, the three waveguides exist simultaneously (see the cross-sectional view in FIG. 10), achieving efficient coupling of the TM0 mode of the first waveguide 110 and the TE0 mode of the second waveguide 120 and the corresponding secondary light path waveguide 130. Outside the coupling region, the secondary light path waveguide 130 gradually narrows until it no longer exists (see the cross-sectional view in FIG. 11), and the distance between the first waveguide 110 and the second waveguide 120 in the third direction gradually increases, avoiding coupling of the TE0 modes of the two waveguides, thereby achieving efficient polarization rotation and splitting. Figure 4 , Figure 5 As shown in FIG. 12, the full-etch silicon nitride polarization-rotating beam splitter 100 based on a dual-layer three-waveguide structure is shown. The device structure is shown in FIG. 13. Figure 3 As shown in FIG. 14, the first waveguide layer of this embodiment includes the first waveguide 110, and the second waveguide layer includes the second waveguide 120 and the secondary light path waveguide 130. The secondary light path waveguide 130 is located on the side of the second waveguide 120. Figure 4 As shown in FIG. 15, the full-etch silicon nitride polarization-rotating beam splitter 100 based on a dual-layer three-waveguide structure is shown. The device structure is shown in FIG. 16. Figure 5 As shown in FIG. 17, the first waveguide layer of this embodiment includes the first waveguide 110, and the second waveguide layer includes the second waveguide 120 and the secondary light path waveguide 130. The secondary light path waveguide 130 is located on the side of the second waveguide 120. Embodiment 3
[0067] As shown in FIG. 18, the full-etch silicon nitride polarization-rotating beam splitter 100 based on a dual-layer three-waveguide structure is shown. The device structure is shown in FIG. 19. Figure 7 As shown in FIG. 20, the first waveguide layer of this embodiment includes the first waveguide 110, and the second waveguide layer includes the second waveguide 120 and the secondary light path waveguide 130. The secondary light path waveguide 130 is located on the side of the second waveguide 120. Figure 8 As shown in FIG. 21, the full-etch silicon nitride polarization-rotating beam splitter 100 based on a dual-layer three-waveguide structure is shown. The device structure is shown in FIG. 22. Embodiment 4
[0068] As shown in FIG. 23, the full-etch silicon nitride polarization-rotating beam splitter 100 based on a dual-layer three-waveguide structure is shown. The device structure is shown in FIG. 24. Figure 9As shown, the embodiment is a full-etch silicon nitride polarization-rotating beam splitter 100 based on three layers of three waveguides. The first waveguide layer includes a first waveguide 110, the second waveguide layer includes a second waveguide 120, and the third waveguide layer includes a sub-path waveguide 130. The sub-path waveguide 130 at least partially overlaps the second waveguide 120 in the first direction. Embodiment 5
[0069] As shown, the embodiment is based on Embodiments 1-4, and the sub-path waveguide 130 is divided into multiple sub-waveguides. Figure 6
[0070] In this application, unless otherwise explicitly specified, the first feature is "on", "over", "above", and "on top of" the second feature, "under", "below", and "underneath" the second feature, or the first feature and the second feature can be in direct contact, or the first feature and the second feature can be in indirect contact through an intermediate medium. Moreover, the first feature "over", "above", and "on top of" the second feature can be directly above or obliquely above the second feature, or simply means that the horizontal height of the first feature is higher than the horizontal height of the second feature. The first feature "under", "below", and "underneath" the second feature can be directly below or obliquely below the second feature, or simply means that the horizontal height of the first feature is less than the horizontal height of the second feature.
[0071] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations encompassed by the claims. Various modifications and changes can also be made on the basis of the above embodiments without departing from the scope of the disclosure. Similarly, any combination of the technical features of the above embodiments can also be made to form additional embodiments of the application that can not be explicitly described. Therefore, the above embodiments only express several implementations of the application, and do not limit the protection scope of the patent of the application.
Claims
1. A polarization-rotating beam splitter, comprising: a first waveguide layer and a second waveguide layer layered in a first direction; at least one waveguide on each waveguide layer; a first waveguide on the first waveguide layer, the first waveguide comprising an input end and a first output end; a second waveguide on the second waveguide layer, the second waveguide comprising a second output end; the second waveguide being asymmetric to the first waveguide in the first direction; light entering the first waveguide from the first input end being coupled through the first waveguide and the second waveguide and output along the first output end and the second output end. 2.The polarization-rotating beam splitter of claim 1, wherein: the first waveguide comprises an input section, a first coupling section and a first output section connected in a second direction in sequence; wherein the input section, the first coupling section and the first output section have the same size in the first direction, and the first coupling section has a size in a third direction larger than that of the input section or the first output section in the third direction; wherein the first direction, the second direction and the third direction are perpendicular to each other. 3.The polarization-rotating beam splitter of claim 2, wherein: the size of the first coupling section in the third direction is less than or equal to 3μm. 4.The polarization-rotating beam splitter of claim 2, wherein: a first transition section is provided between the first coupling section and the input section, the first transition section gradually increasing in size from the same size as the input section to the same size as the first coupling section in the third direction; a second transition section is provided between the first coupling section and the first output section, the second transition section gradually decreasing in size from the same size as the coupling section to the same size as the output section in the second direction. 5.The polarization-rotating beam splitter of claim 2, wherein: the second waveguide comprises a second coupling section and a second output section connected in the second direction; the second coupling section and the second output section have the same cross-sectional size; and in the third direction, the distance between the first output section and the second output section is greater than the distance between the first coupling section and the second coupling section. 6.The polarization-rotating beam splitter of claim 5, wherein: the distance between the second coupling section and the first coupling section in the first direction is less than or equal to 500nm. 7.The polarization-rotating beam splitter of claim 5, wherein: a third transition section is further provided between the second coupling section and the second output section. 8.The polarization-rotating beam splitter of claim 2, further comprising: at least one secondary waveguide, each of the secondary waveguides being located at a side of the second waveguide, and each of the secondary waveguides having a distance from the second waveguide in the first direction less than or equal to 500nm and a distance from the second waveguide in the third direction less than or equal to 500nm. 9. The polarization-rotating beamsplitter of claim 8, wherein: the at least one sub-path waveguide is located on the first waveguide layer and on a side of the first waveguide that is proximate to the second waveguide.
10. The polarization-rotating beamsplitter of claim 8, wherein: the at least one sub-path waveguide is located on the second waveguide layer, and all of the sub-path waveguides are located on the same side of the second waveguide.
11. The polarization-rotating beamsplitter of claim 8, further comprising a third waveguide layer located on a side of the second waveguide layer that is distal from the first waveguide layer, and wherein the at least one sub-path waveguide is located on the third waveguide layer.
12. The polarization-rotating beamsplitter of claim 8, wherein: the first waveguide, the second waveguide, and the sub-path waveguides each have a dimension in the first direction of 200-500 nm.